Flow sensing may be used in a variety of different applications, such as to determine flow velocity of a fluid, such as gas (e.g., air) or liquid, through a pipe or tube. For example, flow sensing may be used in ventilation and respiration machines to detect and control the level of air flow. As another example, flow sensing may be used in gas metering systems, such as for residential applications.
The determination of the fluid flow may be affected by many different factors, such as temperature, moisture variations, or the type or density of fluid, among others. Some conventional systems are not satisfactorily responsive to these different factors. As a result, the outputs of these systems may drift and cause readings that are not accurate. Additionally, the robustness of these systems suffer.
In a medical setting, when using ventilation and respiration machines such as continuous positive airway pressure (CPAP) machine and a variable positive airway pressure (VPAP) machine, it is important to be able to determine accurately the flow rate of ventilation and/or respiration. For example, the air supply pressure from these machines is varied based on whether the person is breathing in or out, such as during inspiration and expiration phases of the respiratory system. By properly controlling the air flow during different phases of breathing, a more comfortable process results. The more comfortable the ventilation and/or respiratory machine is to a person during use, the more likely the person is to continue to use the ventilation and/or respiratory machine. Users of ventilation and/or respiratory machines may unilaterally decide to cease use of the machine as a result of the machine being uncomfortable during operation, such as when an appropriate air pressure is not supplied. However, due to the complex nature of breathing and the change in direction and speed of air flow during breathing (as well as other factors), it is very difficult to determine flow rates.